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957 Posts
I highly recommend Randakk’s rebuild kit. Better quality parts and only the parts you need.
New CX500 Owner from Fredericton, NB, Canada
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When reusing rubber o-rings or parts diaphragms etc steer clear of WD-40 and similar penetrating oils as they expand and swell the rubber. The last time I did a did a brake master cylinder and caliper rebuild, I used brake cleaner to clean and petroleum jelly or Vaseline to freshen the rubber. And I reused a fuel pump diaphragm on a 19 horse Briggs & Stratton using Vaseline. I couldn't get the new rubber to work then I pinched it so I went back to the old rubber lubed it up and it worked first time. Just a thought, unless someone has objections to using vaseline.
I wouldn't rule out the fuel petcock diaphragm either but I think it's more likely the carb issues. You could rule out the fuel petcock diaphragm by running a gasoline hanger bottle directly to the carbs. If a fuel petcock diaphragm is perforated and just the right way it would allow just a certain amount of fuel to fill the bowls when you're accelerator uses up that fuel it would shut down until more fuel was put into the bowls. More likely your carb issues but who knows?
There's an inline fuel filter that I can verify has fuel in it, would that be enough to eliminate this?
Now the way it's run the lines are kinked a tiny bit so I could try and straighten that out too but it was this way with the previous owner too.
Really it's all just speculation until I get the carbs rebuilt, so just ordered the cheap kit ($12 US for 2 carbs) as a starting point. The Randakks one is $85-$105 + $42 US shipping to Canada and the bike only cost me $390 US! I get there's cost in restoring a vintage bike but I don't want to go all-out on each part just yet.
I would think that if the fuel filter retains fuel while it's stumbling that that should rule out the fuel petcock as a problem. Even on that 19 horsepower Briggs that I mentioned using vaseline on the diaphragm, I could tell that the diaphragm wasn't working because there was no fuel flowing through the fuel filter. When the diaphragm was sealed right and pulsating right then the fuel started to flow and would shut off when the fuel bowl was filled and the float had seated the needle valve
I almost always bring up the fuel petcock valve as a possibility because one time I had a gl500 that would starve itself of fuel on the road then start back up etc. After cleaning the carbs twice swapping coils installing new igniters and probably other things I sold it to another fellow more mechanically inclined than I, who basically repeated what I did. He ended up selling it to another fellow in his neighborhood who found the culprit problem of a perforated diaphragm in the petcock valve. It was a pretty nice gl500 that I probably would have kept if not for the poor running issues.
Well, got to g for now,, take care and good luck.
I almost always bring up the fuel petcock valve as a possibility because one time I had a gl500 that would starve itself of fuel on the road then start back up etc. After cleaning the carbs twice swapping coils installing new igniters and probably other things I sold it to another fellow more mechanically inclined than I, who basically repeated what I did. He ended up selling it to another fellow in his neighborhood who found the culprit problem of a perforated diaphragm in the petcock valve. It was a pretty nice gl500 that I probably would have kept if not for the poor running issues.
Well, got to g for now,, take care and good luck.
1978 CX500, 1982 GL500 Silverwing Interstate, 1980 CX500 Custom
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49 Posts
I am probably way off base here, but if you have the carbs off anyway - why not do a compression check on each cylinder. I think you mentioned possibly replacing the Valve Cover gasket due to over tightening. Maybe there's more to it on that cylinder?
The compression/leak test will reveal condition on valves, piston rings, or maybe head gasket. If the oil was nice an black when you drained it, then it probably won't be a head gasket leaking coolant into the oil channels.
But bad valves/rings could mean oil is accumulating and or getting burned, and if only running for very short periods could just pool in the collector.
Even if this isn't the cause - doing the test will give you some peace of mind about the state of each cylinder. If memory serves, compression with a wide open throttle should be above 150 - 190 psi, with both cylinders in a close range to each other.
Good luck, looks like it has the potential to be a nice bike!
The compression/leak test will reveal condition on valves, piston rings, or maybe head gasket. If the oil was nice an black when you drained it, then it probably won't be a head gasket leaking coolant into the oil channels.
But bad valves/rings could mean oil is accumulating and or getting burned, and if only running for very short periods could just pool in the collector.
Even if this isn't the cause - doing the test will give you some peace of mind about the state of each cylinder. If memory serves, compression with a wide open throttle should be above 150 - 190 psi, with both cylinders in a close range to each other.
Good luck, looks like it has the potential to be a nice bike!
Tracked down a compression gauge from a buddy, so I'll give that a check along with all of the other non-engine-removing things I can think of. I have no idea why the left valve cover was off in the first place to get stripped/resealed so checking the compression is a great suggestion, thank you!
If compression is fine on both sides I'll probably just leave them in place for the time being, but if I need to check the valves or anything I'll pick up at least one gasket kit as the left one already looks like it was sealed up a bit with liquid gasket and won't likely survive another opening.
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15,165 Posts
FWIW, similar problems have been traced to inline fuel filters that don't have the outlet lower than the inlet so when more fuel is needed as the revs increase it can't get to the outlet fast enough.
But if I found the insides of the carbs looking like that I'd want to clean them thoroughly before I started looking elsewhere too.
And if there was fuel in the tank I'd be thinking about ways to clean that and the petcock too.
BTW: Welcome to the forum and welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and the Previous Owners may or may not have done the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for mode
But if I found the insides of the carbs looking like that I'd want to clean them thoroughly before I started looking elsewhere too.
And if there was fuel in the tank I'd be thinking about ways to clean that and the petcock too.
BTW: Welcome to the forum and welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and the Previous Owners may or may not have done the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel (old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet). If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for mode
So I thought I had sorted out the left cylinder firing, but it seems like I'm still only getting the right one, pull the plug cap on the left no change, pull the one on the right and it dies. It seems to have spark and I've swapped the ignitors and it's the same so still could be fuel getting to the carb, if I spray carb cleaner into the left carb I get a nice rev boost so I think that's a sign towards fuel flow in the left carb is it not? Sprayed into the right and it stalls too, probably too rich.
I'd like to re-route this fuel line sometime to get it out of the way a bit and take out the kink, on the to-do list especially with comments around flow but I think we're still in carb-town here! Also doesn't appear to be original petcock as there's no vacuum or vent hose.
![IMG_2789.jpeg]()
I'd like to re-route this fuel line sometime to get it out of the way a bit and take out the kink, on the to-do list especially with comments around flow but I think we're still in carb-town here! Also doesn't appear to be original petcock as there's no vacuum or vent hose.
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15,165 Posts
That sounds like a plugged jet or passage.
Replacing the original vacuum petcock with a non-vacuum one is a pretty common solution to the hard starting problem associated with vacuum ones (fuel evaporates from the bowls and after a few days there isn't enough left for starting so you have to crank the engine fast enough to produce sufficient vacuum to open the petcock's vacuum valve long enough to let the bowls re fill before it can start). It should be fine as long as the barb for the vacuum line (usually on the left side of the right carb's outlet) is capped.
Some people recommend adding an inline fuel filter to prevent rust/debris from the tank from getting into the carbs but that is only a band aid fix; The proper solution is to make sure the tank is clean and have it epoxy lined if it is rusty.
As I said before, if I found stuff like that inside the carbs I'd want to look inside the petcock & tank too. The first thing to do is remove the petcock and look for dirt in the filter that is supposed to be inside the tank over the petcock's inlets. If it looks clean you probably don't need the external filter.
Replacing the original vacuum petcock with a non-vacuum one is a pretty common solution to the hard starting problem associated with vacuum ones (fuel evaporates from the bowls and after a few days there isn't enough left for starting so you have to crank the engine fast enough to produce sufficient vacuum to open the petcock's vacuum valve long enough to let the bowls re fill before it can start). It should be fine as long as the barb for the vacuum line (usually on the left side of the right carb's outlet) is capped.
Some people recommend adding an inline fuel filter to prevent rust/debris from the tank from getting into the carbs but that is only a band aid fix; The proper solution is to make sure the tank is clean and have it epoxy lined if it is rusty.
As I said before, if I found stuff like that inside the carbs I'd want to look inside the petcock & tank too. The first thing to do is remove the petcock and look for dirt in the filter that is supposed to be inside the tank over the petcock's inlets. If it looks clean you probably don't need the external filter.
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4,185 Posts
The carb spray in the left carb resulting in a rev boost shows that you have a good spark on the left cylinder and lack of fuel.
I'll put those things on the list! Gas in the inline filter has looked clean, and I can't go by the old filter as everything went gross in there likely from sitting. Inside of the tank is pretty rusty as when it was left for 2 years it only had about 1/6 tank of gas in it, but I can check the petcock filter too, shouldn't be much work to drain the tank again, just have to listen to my wife complain about me smelling like gas again!
Vacuum line on the right carb is definitely capped off (with a screw in the hose - probably do something a little nicer looking)
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5 Posts
Oil leak could be the shifter seal...easy fix.
Oh when I picked it up there was a small bit of oil on the floor from the shifter seal for sure, that’ll get replaced but I’m no longer thinking it’s oil in the exhaust but condensation mixed with carbon in the exhaust since it’s quite cool here and upon further inspection it seems more like water mixed with sediment than oil.
Can you get those seals right from a Honda power sports dealer, or just easier to get online?
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6,967 Posts
Honda dealer here has to order most of my parts, but I dont pay shipping
Deleted comments about a 10% discount from an American Honda powersports seller. I noticed that you're from Canada and the shipping duty cancels and destroys any benefit of any discount in less it would be a large order {period}
Which is why I'd happily order it at the dealer! Plus being in Canada places in the US that offer "Free US Shipping" usually translates to $5-10 (if you're lucky) or $50-180 for shipping to Canada because they use DHL or something else that's crazy expensive, or they just want to gouge.
UPDATE: Called the dealer - $6.50 CDN, no shipping. Not quite as good as the $2.53US on the discount honda parts site, but I'll take it!
Friend's compression gauge was for oil and transmission pressure, but it turns out NAPA has one you can "rent" for free, basically a refundable deposit under a tool loan program so I'll be doing that, hoping they have a carb sync tool as well in the same inventory.
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